3. Indian Ocean Dipole; IOD
is a variation of the sea surface temperature in the Indian Ocean. In normal conditions, the eastern side of the Indian Ocean or Southeast Asia is a region of warm water that is driven by Kelvin waves blowing cold water masses from the west to the southeast, causing abnormal cooling of the sea surface temperature in the southeast and the unusual warming of the surface water temperatures west of the Indian Ocean equator. In general, the IOD indicator is usually based on the Dipole Mode Index (DMI), which is water temperature difference between the west and southeast of the Indian Ocean. DMI is used to refer to the IOD. If the IOD is positive (negative), the east coast of the Indian Ocean in Southeast Asia will be dry (heavy rain) and the west side will have heavy rain (dry) as shown in Figure 5-19. The most positive IOD occurred in October 2006, while the negative occurred in July 2016.
IOD has an impact on Thailand ‘s climate – both temperature and rainfall, but the mechanism or its linkage cannot be clearly proven like the ENSO. The effects of the IOD may be part of the increase or decrease of the ENSO effect.